|
1. Definition
| Name |
SLOPE
ASPECT |
| Brief
definition |
Aspect is defined as the
orientation of the earth's surface with respect to the sun.
 |
South-facing
slope in the island of Lesvos highly affected by desertification
(photo by C. Kosmas) |
|
| Unit
of measure |
Direction
with respect to the magnetic north |
2. Position
within the logical framework DPSIR
3. Target and
political pertinence
| Objective |
Contribution
to the definition and mapping of ESAs and assessment of the
desertification risk of an area. |
| Importance
with respect to desertification |
Variation in slope exposure
and elevation influence the distribution of energy, meteoric
water, plant nutrients and vegetation by varying: (a) the
exposure of the soil to wind, (b) the exposure of the soil
to precipitation, (c) the conditions for natural drainage,
(d) the conditions for runoff and erosion, (e) the conditions
for accumulation and removal of deposits by wind. In the Mediterranean
region, the rates of soil erosion measured along south-eastern-
and south-western-facing hillslopes is twice as much as or
even higher than in north-eastern- and northwester-south-facing
slopes under various types of vegetation cover (see figure).
 |
Distinct
erosion patches measured along hilslopes with various
types of vegetation located at north and south-facing
slopes (P=pines, B=evergreen oak, oak, O=olives, Q=deciduous
oak, A=perennial shrubs) (Kosmas et al., 1999) |
Therefore, southern exposed
slopes usually are more sensitive to desertification than
northern exposed slopes.
|
| International
Conventions and agreements |
The CCD emphasizes
that combating desertification must be tackled within the general
framework of actions to promote sustainable development.
|
| Secondary objectives
of the indicator |
Within the
ESA model investigation of the individual processes linked to
land degradation and desertification. |
4. Methodological
description and basic definitions
| Definitions
and basic concepts |
Aspect affects the microclimate
of an area by regulating the angle and the duration at which
the sun's rays strikes the surface of the soil. In the Mediterranean
region, slopes with south-eastern and south-western-facing
aspects are warmer and have higher evaporation rates and lower
water storage capacity than north-eastern- and northwester-facing
aspects. Therefore, a slower recovery of vegetation is expected
in southern aspects and higher erosion rates than in northern
aspects.
It should be noted that
organic matter content of the top 10 cm of soil is greater
in north-facing slopes than in south-facing slopes. This is
generally considered to be the result of higher soil temperatures
on south facing-slopes causing more rapid organic mineralization.
However, the greater intensity of isolation in south-facing
slopes exposes the growing plants under greater moisture stress
reducing biomass production.
|
| Benchmarks
Indication of the values/ranges of value |
|
| Methods
of measurement |
Aspect
can be defined by using a compass or by assessing the relative
earth's surface with respect to the magnetic north. |
| Limits of the
indicator |
This indicator,
despite its importance on microclimatic conditions and vegetation
performance, it is topographically dependent. There is an interrelation
with elevation. |
| Linkages with
other indicators |
Rainfall,
Slope gradient, Soil
depth, Rock fragments,
Water storage capacity. |
5. Evaluation
of data needs and availability
| Data
required to calculate the indicator |
Data
on aspect can be obtained from digital elevation models (DEM)
or by simple measurements in the field.
|
| Data
sources |
Necessary
data are usually available and accessible and the cost/benefit
ratio is reasonable. |
| Availability
of data from national and international sources |
Data can be
obtained from various regional, national or international institutions
involved in collecting topographical data. |
6. Institutions
that have participated in developing the indicator
| Main institutions
responsible |
Agricultural
University of Athens
|
| Other contributing
organizations |
Universities
of Lisbon, Murcia, Basilicata, Amsterdam, Leeds
|
7. Additional
information
| Bibliography
|
Kosmas,
C., Kirkby, M. and Geeson, N. 1999. Manual on: Key indicators
of desertification and mapping environmentally sensitive areas
to desertification. European Commission, Energy, Environment
and Sustainable Development, EUR 18882, 87 p. |
| Other references |
Kosmas, C., Danalatos,
N.G, and Gerontidis, St. 2000. The effect of land parameters
on vegetation performance and degree of erosion under Mediterranean
conditions. Catena, 40:3-17.
Ruiz-Flano, P., Garcia-Ruiz,
J.M. and Ortigosa, L., 1992. Geomorphological evolution of
abandoned fields. A case study in the Central Pyrenees. Catena,
19:301-308.
|
| Contacts Name
and address |
Agricultural
University of Athens
Dr Constantinos Kosmas
email: lsos2kok@aua.gr |
|
